Structure 2.2 - Covalent Model 
Lewis Structures

Understanding electron pairs and molecular geometry. In order to understand molecular geometry, it is important to first understand the concept of electron pairs. In an atom, electrons are arranged in energy levels or shells. The outermost shell, known as the valence shell, is the most important for determining the chemical behavior of an atom. The valence shell contains the valence electrons, which are the electrons involved in bonding with other atoms. According to VSEPR theory, electron pairs in the valence shell of an atom repel each other. This repulsion causes the electron pairs to try to get as far apart from each other as possible. As a result, the atoms in a molecule will arrange themselves in a way that minimizes this repulsion. There are two types of electron pairs: bonding pairs and non-bonding pairs. Bonding pairs are the electrons involved in covalent bonds, which are the sharing of electrons between atoms. Non-bonding pairs, also known as lone pairs, are the electrons that are not involved in bonding and are located on a single atom. The arrangement of these electron pairs determines the molecular geometry of a molecule. For example, if a molecule has two bonding pairs and no lone pairs, it will have a linear shape. If a molecule has three bonding pairs and no lone pairs, it will have a trigonal planar shape. By knowing the number and arrangement of electron pairs in a molecule, scientists can predict its shape and make predictions about its chemical properties and behavior.